Portable electrical tool



Feb. 5, 1935. .F. KRATZ in" AL PORTABLE ELECTRICAL TOOL Filed April 4, 1932 Q I IHHI Patented Feb. 5, 1935 i Q I UNITED STATES PATENT OFFICE I 1,990,035 PORTABLE ELECTRICAL T001.

Franz Kratz and Ernst Baumgratz, Stuttgart,

Germany, assignors to Robert Bosch Aktiengesellschaft, Stuttgart, Germany Application April 4, 1932, Serial No. 603,133

- In Germany July 27, 1931 14 Claims. (01. 172-36) The present invention relates to electrically needle roller-bearings 13 and carries a removdriven hand directed machines and more parable small grinding disc 14. On the rear side ticularly to an electrically driven hand grinding oi the extension '7 is fastened a handle 15, in machine. I which is fitted a switch 16 for the current cir- In order to enable small surfaces, for instance, cult of the motor 1, the base part a of a U-shaped 5 of steel or other material, to be quickly and neatly stirrup a secured to handle- 15 being secured or finished, grinding wheels driven by compressed connected to bearing bracket or sleeve 8 by means air are already employed in which the wheel of nut 10 screwed on the threaded rear end of spindle has a speed of 50,000 revolutions or more the bearing brac et, said bracket Passing through 10 per minute. As however, a source of compressed an opening a in the base part of the stirrup. 10

- air is frequently not available, the use of these The handle is thus secured or directly connected tools is limited. to the spindle bearing bracket or sleeve at a The electric hand-motor grinding-machines point closely adjacent one end of the tool spindle hitherto generally used are indeed provided at and (IO- with e axis thereof w y the 5 one part with gearing by whi h in a k wn distance between the working end of the tool construction the speed of the tool spindle is spindle and the point where t e d of the brought up to about.12,500 revolutions per minp holds the ach (the handle) is reute. In this ca'se,.the motor is so heavy that duced to a minimum; furthermore, the handle is the machine can only be held with both hands. arran d a sid of t motor- This a a Consequently, its handling is very inconvenient. t D OVideS a Very comp Well-balanced tO 20 Furthermore, the grinding disc in order to have which is easily handled d u ded, notwitha suflicient peripheral speed must have a large s n the extremely high Speeds t w ch both diameter, so that small surfaces cannot be treated the motor and spihdlerotete- TWO easing ps by it. 17 and 18 of insulating material enclose the ma- The object of the invention is to produce a ehine- In the bottom of the p holes '19 2: small electrical machine which is equal to the are Provided, and in the twO a -b ackets compressed air tool in ma i ul tion d capac- 2 and 3 are passages 20, which enable the motor ity. According to the invention, the .motor, 1 to b sufficiently Cooled y t a drawn in whilst being ofsmall diameter and weight, which by the fan e p 17 has t ll 21 Surenables it to be conveniently held with one hand, rounding the holder The from the a 30 has a high speed when running u de no b d 6 emerging from the tube 21 cools the tool spindle of about 8,000-12,000 revolutions per minute, and 9, a the e time blows away t dust is so geared to the tool spindle that this latter which arises n grindinghas a speed of 30,000 to 50,000 and more revolu- The belt P y 5 ves at t e Same time as tions per minute when running under no load, a fly-Wheel disc in order o compensate Varie- 35' in order t ttai fli i t peripheral speed tions in load on the motor in intermittent workfor a tool disc of small diameter. After slackening t p- 0, the ot An example of construction of the invention in which is accessible through an opening n the is Shown in the drawing in which handle 15. the distance of the holder 8 from the Fig. 1 is, a longitudinal sectional view, and motor shaft 4 can be altered by the screw 40 Fig 2 i sectional i t k on t i in order to enable the tension of the belt 22 on 2-2 of Fig. 1, looking in the direction of the the two belt Pulleys 5 and 12 to b adjusted. arrows, the lower casing cap being removed. The motor has a speed When running w t ut A u l tri hand motor 1 of t usual load of about 10,000-l2,000 revolutions per min- 5 cylindrical construction has a diameter of about lite, which is increased by the belt gearing t 4" 5 cm. and a length of about 8.5 cm. The motor about 40,000 to 50,000 revolutions D minuteshaft 4, mounted in the two bearing brackets Consequently, even when using small d g 2-and 3, carries a belt pulley 5, which is condiscs, 3 suflioiently high peripheral p ed can t t so as t t t, t Same time also as be attained for instance of 20 metres per second. a fan disc 6. The bearing bracket 2 has on its g g g r g fim t 5 lower side an extension '7, in which is secured er 9 .1ame r w w a a holder or bearing sleeve or bracket 8 for a gg'gg i igf Instance m the mtental gnndmg of tool p dl 9 y m n f s p-n 0 and As will be seen from the drawing, the handle an ad ustlng screw 11. The spindle 9 on which H 15 is connected to the machine in theprolongation a b t P l y 12 1s fastened 15 mounted in three of the tool spindle 9; therefore, the tool can be i pulleys.

conveniently directed by the hand to the place which is to be operated on; Owing-to its small dimensions, the motor is of low weight, so'that the weight of the complete machineincluding theconducting cable isconsiderablybelow 1,000grams. The machine is therefore easy to handle. The motor can be easily connected by a cable to the electric lighting mains existing in any workshop. This cable is considerably lighter and more portable than the air-pipe which is necessary in known compressed air tools.

If desired, the machine can also be fastened by a supporting yoke-or the like on the slide-rest of a lathe, or other alterations may be made. For example, a belt pulley drive can be provided at both ends of the motor shaft, and correspondingly the tool spindle is then fitted with two belt It will be obvious that instead of the grinding disc other tools can be secured in the spindle 9. Further, one end of the motor shaft can be constructed as-a holder for a milling cutter, drill or other tool which does not requirev such a high speed of rotation.

7 comprising a'casing; an electric motor mounted in said casing, a tool spindle rotatably mounted in said casing, gear means connecting said spindle and said motor, fan means mounted on said motor shaft, and'a cover enclosing said fan means and having a tubular extension enshrouding said spindle so that the fan means directs a blast of air upon a tool connected to said spindle.

3. An electrically driven hand directed machine comprising a casing, an electric motor mounted in said casing, a spindle, a housing for said spindle adjustably secured to said casing, a pulley on the shaft of said motor, a pulley on said spindle, a belt connecting said pulleys, and means to secure said housing in the adjusted position to maintain the correct tension on said belt.

4. An electrically driven hand directed machine comprising a casing, an electric motor mounted in said casing, a tool spindle, a housing for said spindle, means for adjustably securing said housing to, said casing, needle roller bearing means supporting said spindle in said housing, a belt pulley connected to said motor constructed to operate as a flywheel and fan simultaneously, abelt pulley on said spindle, a belt connecting said pulleys, and a cover enclosing said pulley and said spindle housing to direct a blast of air upon said tool spindle.

5. A portable electrically driven machine for performing grinding and similar operations at high speed and which is light enough and small enough to be supported and operated by one hand,

said machine comprising a casing, an electric motor mounted in said casing and at one side thereof to rotate at 8,000 to 10,000 revolutions per minute when runing light, a tool spindle rotatably mounted in said casing at the other side thereof, gear transmission means connecting said motor to said spindle to rotate said spindle at 30,000 to 50,000 revolutions per minute when running light, and a handle secured to said casing at'a point colinear with the axis of said spindle and alongside of said motor.

6. A portable electrically driven machine for performing grinding and similar operations at high speed and which is light enough and small enough to be supported and operated by one hand, said machine comprising a casing, an electric motor mounted in said casing and at one side thereof to rotate at 8,000 to 10,000 revolutions per minute when runninglight, a tool spindle rotatably mountedin said casing at the other side thereof, and transmission means in said casa driving belt connecting said pulleys'to rotate I said spindle at 30,000 to 50,000 revolutions per minute, and a handle secured to said casing and alongside of said motor at a point closely adjacent one end of said spindle and co-linear with the axis thereof.

7. A portable electrically driven machine for performing grinding and similar operations at high speed comprising a casing, an electric motor mounted in said casing, a tool spindle mounted in said casing and along side of said motor, means in said casing connecting said tool spindle at a point closely adjacent one end of said tool spindle and co-linear with the axis thereof.

8. An electrically-driven hand directed machine comprising a mounting, a tool spindle rotatably mounted therein, a handle secured to said mounting closelyadjacent one end of saidtool spindle and in alinement with the axis thereof, an electric motor mounted in said mounting alongside of said tool spindle and'handle, and gear means connecting said motor and said tool spindle.

9. A portable electrically driven machine for performing grinding and similar operations at high'speed comprising a tool spindle, mounting means including a handle for rotatably mounting cent .one end of said tool spindle and in alinement with the axis thereof, and an electric motor for rotating said tool spindle, said motor being secured to said mounting means at one side of and out of alinement with the axis ,of said 11. An electrically driven hand directed ma-- chine comprising a casing, an electric motor '25 to said motor, and a handle secured to said casing said tool spindle, said handle being closely adja-'- mounted therein, a motor bearing bracket provided with a lateral extension, a tool spindle, a bearing sleeve for said spindle secured to the exten:

sion of said motor bearing bracket, gear means connecting said motor and said spindle, and a handle secur'edto said spindle. bearing sleeve.

12. A portable electrically driven machine for performing grinding and similar operations at high speed comprising a casing, an electric mo said casing, a motor in said casing. a spindle driven by said motor and extending along said bearing sleeve, a cooling fan driven by said motor,

and an enclosing sleeve arranged around said 5 bearing sleeve for guiding the air from said tan along the bearing sleeve.

14. An electrically driven portable tool com-- prising a casing, a bearing sleeve extending from said casing, a motor in said casing, a spindle 1o driven by said motor and extending along the bearing sleeve, an enclosing member arranged around and spaced from the bearing sleeve so as to form an air e, and a cooling fan driven by the motor and adapted to draw air through the motor and to discharge the same through the passage formed between said member and said sleeve.

' FRANZ KRA'IZ.

ERNST BAUMGRA'IZ. 

